Unmanned aerial vehicles (UAVs) commonly include multiple, such as four or more, fixed-pitch rotors, driven by controllable electric motors, providing take-off, hover, and landing capabilities with a high degree of freedom. The UAVs often use differential drives, which direct one or more of the rotors to generate different levels of thrust in order to control pitch, yaw, and/or roll, and thus generate a net thrust vector of the UAV. The rotors of some UAVs are driven by electric motors powered by an onboard battery, but such UAVs do not tend to have long-range capabilities without requiring refueling along the way. In contrast, rotors driven by engines that use higher density fuel sources, such as an internal combustion engine, have an increased range but are heavy, more expensive, less reliable, and noisy.